It's sometimes hard for people to separate this figure from the cutting activities they've just been engaged with. Make sure you're clear about how the figure was constructed; it might help to create it yourself. First, start with the triangle. Find midpoints D and E and connect them. Then extend that segment to twice its length. Recall what we know: AD = DC (D is a midpoint); BE = EC (E is a midpoint); DE = EF (we made the figure that way); angle DEF is 180° (we made it a straight line). That's all we know.